This invention relates to a vehicle maneuvering control device which can control a running vehicle at a proper speed on a curved road.
Recently such vehicle maneuvering control devices have been developed as follows: On a vehicle, a navigator or the like is installed. A radius of curvature of a curve emerging ahead of the driver is calculated based on the processed map information obtained from the navigator. Based on, for example, the detected radius of curvature and the vehicle speed, the warning/deceleration control is made while judging whether the vehicle can corner the upcoming curve or not.
For example, the Japanese Patent Laid-open No. 194886/1996 discloses a control device responsive to the upcoming road condition. In this device, emerging curves are detected based on information from a navigator. When a curve is detected, the device takes into account both the curvature and vehicle speed, and judges whether the present vehicle speed will be too high when entering the corner. If the speed is too high, a warning is set off, or the running condition of the vehicle is adjusted.
The judgment according to the prior art is made as follows: A corrected value based on vehicle speed is added to a predefined target lateral acceleration based on steering angle and the vehicle speed, to obtain an allowable lateral acceleration for approaching the curve. An allowable approaching speed is calculated based on the obtained allowable lateral acceleration and the radius of curvature. When comparison between the present speed and the obtained allowable approaching speed reveals that the present speed is higher than the allowable approaching speed, judgment is made that the present speed is too high.
In general, when road slope, road surface friction coefficient or other road conditions change, the braking distance and the critical cornering performance of vehicles may change even when the same braking force is applied. Accordingly, the setting of the allowable approaching speed, i.e., a referential judgment value for a vehicle under cornering must be made taking fully account of these factors.
According to the prior art, however, when setting the allowable approaching speed, road slope, road surface friction coefficient and other road conditions are not fully taken into account, so that in a variety of actual running roads, it is difficult to make adjustments in perfect in accordance with the conditions of the road being traveled on.
Furthermore, even when the vehicle speed exceeds the critical speed at which the vehicle can turn the corner, its criticality varies with the distance remaining before entering the corner. The longer the remaining distance, the easier it is to decelerate the vehicle down to the critical speed, but the shorter the distance, the more rapidly the deceleration must be performed.
In the foregoing prior art, however, the device makes judgment by comparing the vehicle speed (the present speed) and the allowable approaching speed under the assumption that the vehicle will continue traveling at the present speed until it reaches the starting point of the emerging curve from the warning set-off point which has been defined as a given distance (depending upon the present vehicle speed) ahead of the curve staring point. Accordingly, to make a more practical and reliable control, the distance up to the curve starting point should be taken into account.